1. Field of the Invention
The present invention relates to commonly packaged multiple memory die, and more particularly to methods of and apparatus for determining unique die identifiers for multiple memory die contained within a common package.
2. Description of Related Art
The packaging of two or more memory die in one package for various purposes is commonplace. The die may be identical or different. In some instances the respective interfaces of the die are partially or fully interconnected, so that a technique is needed for distinguishing among the various die using the pins of the package. This problem is particularly acute where the die are of the same type.
The chip select pins of stacked memory die may be used to distinguish among the die. As disclosed in Spansion Inc., Data Sheet, S70FL256P 256-Mbit CMOS 3.0 Volt Flash Memory with 104-MHz SPI Multi I/O Bus, Revision 05, Jan. 30, 2013, two identical 128 Mb die are stacked with their individual Chip Select inputs bonded to respective pins of the package to form the flash memory device. Such a memory device may be operated as two separate SPI devices on the same SPI bus, in that the user accesses one die of the dual die stack at a time via its respective Chip Select. Disadvantageously, the controller is required to provide and manage multiple /CS control signals. Moreover, the need for two or more chip select pins eliminates Quad SPI and Quad Peripheral Interface (“QPI”) as suitable options for an 8-pin package.
A memory die typically has a unique identifier (“UID”) established at manufacture, typically for production control. An example of a suitable UID is the combination of a device number, process lot number, wafer number, and x and y coordinates of the die, thereby ensuring the uniqueness of the UID. Such a UID could be used to distinguish one die from the other die in a package through a common interface if the UID were known to the external controller. Unfortunately, after the interfaces of the die are interconnected during manufacture, the individual UIDs may not be accessible and therefore may be unknowable to an external controller.
A technique for programming stack positions of memory die in multi-die memory devices after packaging is disclosed in US Patent Application Publication No. US 2009/0085608 published Apr. 2, 2009 in the name of Alzheimer. Each die drives an output signal to a commonly shared output terminal in response to a die identification data bit of the die. Each die also includes an arbitration circuit that generates a control signal in response to the identification bit of one die being mismatched to a corresponding identification bit of the other die. The control signal also programs a stack enable fuse in accordance with certain results of the arbitration.